After IEC tests, we observe two distinct types of dark areas in the EL images of silicon wafer based PV modules, irregularly shaped regions which are the result of cracks in the silicon wafers, and regular rectangular shaped areas which we postulate are due to broken front grid fingers.
In order to identify the mechanism responsible for the dark rectangular regions in the EL images of silicon wafer based PV modules, we investigate a soldered solar cell which exhibits similar rectangular dark areas in its EL image. SEM microscopy reveals that the dark areas in this cell are due to broken fingers caused by contraction of the tin during the soldering process. We hypothesise that a similar mechanism is responsible for the dark rectangular areas seen in the EL images of silicon wafer based PV modules after the accelerated aging tests.